This invention concerns pumps and pump installations in which a liquid level in a tank is repetitively pumped down to a predetermined level by a pump impeller submerged in the liquid. In some installations, the pump is run continuously until the liquid declines to a level where air is introduced into the pump impeller and pumping ceases. As liquid continues to flow into the tank and the level rises to cover the impeller, the pump will again begin pumping liquid but only after a predetermined delay caused by the need for the pump to eliminate air, which can accumulate at the "eye" of the impeller. The liquid is typically highly aerated increasing the tendency to form an air bubble. The impeller will eventually cause the air to be pumped out of the discharge, but this process takes some time such that the liquid level may rise well above the level to be maintained due to the delay in reestablishing prime.
This effect necessitates a greater tank and pump capacity to insure that an overflow condition is not reached and also results in greater fluctuation in the liquid levels in the tank.
In one prior design, the pump is driven by a motor supported above the liquid, the pump volute supported on a sleeve fixed to the motor support and surrounding an extension of the motor shaft driving the pump impeller.
The extension impeller drive shaft is supported at the upper end by the motor shaft or by separate bearing housing, so as to eliminate the need for a sealed submerged shaft bearing. A substantial clearance space is provided between a wall opening through which the impeller drive shaft passes to avoid the need for a bearing.
Such pump installations are often used in handling machine tool coolant containing metal cuttings and abrasive grit. These solids tend to be forced up into the support sleeve through the extension shaft clearance, and can accumulate to a point where the pump must be disassembled to clean out the accumulated solids in the support sleeve interior. Some installations do have sleeve openings located at intermediate heights on the sleeve and still allow accumulation of solids around the shaft and within the lower end of the sleeve.
It is an object of the present invention to provide an impeller design for such pump installations which will rapidly purge air from the impeller such as to quickly begin pumping liquid when the impeller becomes submerged in liquid.
It is another object of the present invention to provide an improvement for such pump installations which will purge the sleeve interior of solids forced up into the sleeve to eliminate the need for periodic disassembly for cleaning.